1. Field of the Invention
The present invention generally relates to a battery pack unit, a control method for the battery pack unit, electronic equipment, and recording media. More particularly, the invention relates to a battery pack unit having a plurality of battery packs which is suitably used for supplying power to electronic equipment, such as personal computers. The invention is also concerned with a control method for the above type of battery pack unit, electronic equipment driven by power supplied from the above battery pack unit, and recording media on which a program for controlling the above battery pack unit is recorded.
2. Description of the Related Art
FIG. 1 illustrates the configuration in which power is supplied to a personal computer from a battery pack unit according to a technique of the related art. In FIG. 1, a battery pack unit 21, which is formed of four battery packs 21-1 through 21-4, is detachably attached to a personal computer 1.
The personal computer 1 has four switches 12-1 through 12-4, the number of which is the same as the number of battery packs 21-1 through 21-4 attached to the computer 1. One end of each of the switches 12-1 through 12-4 is connected to the positive terminal of each of the battery packs 21-1 through 21-4, respectively. The other ends of the switches 12-1 through 12-4 are connected to each other and are further connected to a port 11. The lines connected to the negative terminals of the battery packs 21-1 through 21-4 are also connected in common to each other within the personal computer 1 and are further connected to the port 11. Moreover, control signals can be individually output to the switches 12-1 through 12-4 from the port 11, thereby separately turning on or off the switches 12-1 through 12-4.
In the state in which the four battery packs 21-1 through 21-4 are connected to the personal computer 1, as discussed above, the personal computer 1 first actuates the switch 12-1 and turns off the other switches 12-2 through 12-4. As a result, power from the battery pack 21-1 is supplied to the individual elements of the personal computer 1 via the port 11.
While the battery pack 21-1 is supplying power, the voltage of the battery pack 21-1 gradually lowers and finally reaches a predetermined reference voltage. Upon detecting the above state, the personal computer 1 turns off the switch 12-1 and turns on the switch 12-2. Then, the battery pack 21-2 starts to supply power.
Similarly, thereafter, every time the voltage of each battery pack reaches a reference voltage, the personal computer 1 sequentially changes the switches 12-1 through 12-4 to obtain power continuously from the battery packs 21-1 through 21-4.
According to the above related art, the provision of the switches 12-1 through 12-4 for the personal computer 1 is necessary to change a plurality of battery packs 21-1 through 21-4. This increases the number of parts and accordingly incurs an increase in the cost. Moreover, the switching devices should be inserted into the power supply path, which generates current loss, resulting in a waste of power.